I wasnt thinking of holding a carabiner in my fist and punching through the glass with an uppercut. Hold carabider in fist and strike downwards - using side of hand not fingers end, the way you would use a through tang knife like the Falkniven F1 to hammer on tent pegs. and with lots of small blows aimed at the window not through it. to crack first not pile all the way through on a big blow and lacerate my hand. The carabiner I have is not symmetrical and has a ridge round the circumferance which gives some of the advantages of a nail but easier to use. It is difficult to hold a nail and strike with it without your fingers sliding down towards the glass. You may not have something available to strike the nail with (if you did obviously the nail would be a better option) and I dread to think of the injuries you could sustain by striking the nail with the heel of your hand. this is emergency use if I actually had something available nearby desinged to break through glass like you see on trains then I would use that in preference

I suppose the best emergency window breaker would be steel tipped heel on a pair of stilletos but unlikely to be available unless you are a) female or b) on your way to a showing of the Rocky Horror Picture Show <img src="images/graemlins/grin.gif" alt="" />

just reread this lot and realised someone else had already explained this was the way to do it - sorry. I was replying very long windedly just to agree with someone <img src="images/graemlins/blush.gif" alt="" /> been a long day!